Ultrasonic absorption and velocity measurements have been made in high-purity liquid sodium, potassium, rubidium, and cesium at temperatures from their melting points to 250°C. Corresponding classical absorption values have also been computed over these ranges of temperature. It has been found that the measured absorption values exceed the classical values by 3%–30%. These excess absorptions are attributed to structural relaxation. The ratio of bulk viscosity to shear viscosity was found to be approximately 2.3 in sodium and potassium, 3.4 in rubidium, and 4 in cesium. Sound velocities are presented as linear functions of temperature. Both observed and classical absorptions are given as quadratic functions of temperature.

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Propagation of ultrasound is investigated in an aqueous solution stratified by two solutes which diffuse at different rates. Both the finger interface and the diffusive interface are considered. Following correction for background absorption, edge effects, and refraction, attenuation of the order of 1.4 dB/cm is observed in the finger interface, while no attenuation is detected in the diffusive interface. The attenuation increases with frequency from 0.8 to 25 MHz. For higher frequencies, up to 42 MHz, the attenuation is constant. The loss is attributed to an as yet unspecified scattering mechanism.

Ultrasonic absorption and velocity measurements have been made in pure liquid alkali metals at temperatures from their melting points to 250°C. Measured absorptions have been found to exceed the computed classical values by 10%–25%. Sound velocities decrease linearly with increasing temperature. The distilled liquid metals were transferred to the measurement apparatus under vacuum (better than 10−4 Torr) and measurements were made under a high-purity argon cover gas. No significant reaction with the cover gas was observed. No bonding agent was needed between the transducer and the clean liquid surface. [This work was supported by the Office of Naval Research.]